In recent years, there has been a growing demand for implementing portable electronic apparatuses, small-sized sensors, or healthcare apparatuses (such as an electronic thermometer and a sphygmomanometer) as thin, lightweight, downsized, and highly water-resistant wearable products, at low cost.
Generally, such an electronic apparatus is formed by mounting a passive component (such as a resistor and a capacitor), an active component (such as an LSI (Large-Scale Integration) and an IC (Integrated Circuit)), a power supply device (such as a battery), a display device (such as an LED (Light Emitting Diode)), and other electronic components (such as a sensor and a switch) on a printed circuit board. Conventionally, such a printed circuit board is manufactured by a method of forming a wire circuit by etching copper foil stacked on a plate made of epoxy resin reinforced by glass fibers (a glass epoxy board) or on a sheet made of polyimide (a flexible printed board). Further, an electronic component is mounted to the wire circuit on this board by using solder, an electrically conductive adhesive, a metal wire, or the like.
However, in the conventional printed circuit board having the wire circuit formed by etching copper foil stacked on a glass epoxy board or a flexible printed board, cost such as material cost and processing cost is high. Further, waste liquid originated from etching processing imposes a heavy load on the environment. Furthermore, it is costly to mount the electronic component using solder, an electrically conductive adhesive, a metal wire, or the like.
In order to mount a plurality of electronic components on such a printed circuit board, it is necessary to provide a space having a predetermined distance or more between the electronic components, resulting in an increased size of the board itself. Further, when the printed board is attached to a structural component such as a case made of resin, a certain amount of space is required between the board and the structural component, resulting in an increased thickness of a product or limited downsizing of a product.
As described above, in order to implement a thinner, downsized, and lower-cost electronic apparatus, a method of assembling an electronic component without using a commonly-used conventional printed circuit board is required.
Japanese Patent Laying-Open No. 7-66570 (PTL 1), Japanese Patent Laying-Open No. 2004-111502 (PTL 2), and Japanese Patent Laying-Open No. 2010-272756 (PTL 3) each disclose a technique for implementing an electronic apparatus without requiring such a printed circuit board, specifically, a technique of embedding an electronic component in a resin molded body such that electrodes are exposed, and forming wires connected to the electrodes on the resin molded body. However, generally, a metal constituting the electrodes and the resin molded body have thermal expansion coefficients different from each other. Accordingly, when a change in shape due to expansion or contraction occurs in the resin molded body, cracks may occur between the resin molded body and the electrodes made of the metal, and disconnection may occur in the wires at positions overlapping the cracks.
As a method for solving such a conventional problem, Japanese Patent Laying-Open No. 2016-201521 (PTL 4) discloses a technique of forming a groove around an electronic component in a resin molded body and providing wires to pass in the groove.
FIG. 5A is a plan view showing a circuit structural body 100 disclosed in Japanese Patent Laying-Open No. 2016-201521. FIG. 5B shows a cross sectional view taken along a line X-X in FIG. 5A and viewed in the direction of arrows. Circuit structural body 100 includes an electronic component 110, a resin molded body 120 embedding electronic component 110, and wires 140 and 141 respectively connected to electrodes 111 and 112 of electronic component 110. A groove 130 is formed around electronic component 110 in resin molded body 120 Wires 140 and 141 are formed by applying an electrically conductive liquid ink to pass in groove 130. Thereby, even when expansion occurs in resin molded body 120 below wires 140 and 141, groove 130 is enlarged accordingly. On this occasion, recesses 142 and 143 formed in wires 140 and 141 are enlarged. Thereby, it is possible to make disconnection of the wires less likely to occur.